Polyvinyl fluoride (PVF) has been manufactured for many years and has found many uses as a protective film or coating over a variety of substrates providing durable and cleanable surfaces. However, polymers with a large amount of vinyl fluoride content cannot be processed from the melt (e.g., molded) because the thermal decomposition of PVF occurs at its melting point of about 200° C. Further, since PVF does not dissolve in most solvents at ordinary temperature due to its high crystallinity and to large amounts of intermolecular hydrogen bonding, casting a film from a solution is also difficult. Consequently, PVF is usually dispersed in a polar solvent having a high boiling point to coalesce and form a film at elevated temperature. This method requires complicated technology and equipment, and does not provide for easy on-site application in the form of paint or coating.
The fluorine atoms in PVF are largely responsible for its properties of excellent weatherability, chemical resistance and mechanical properties. Enhancement of these properties may be achieved with polymers of higher fluorine content. One way to increase polymer fluorine content is to prepare copolymers in which tetrafluoroethylene (TFE) replaces some of the vinyl fluoride (VF). Such dipolymers have been described by Coffman and Ford, U.S. Pat. No. 2,419,009 (1947); Sianesi and Caporiccio, J. Polymer Sci., Part A-1, 6, (1968) 335, and U.S. Pat. No. 3,513,116 (1970). Another way is reported in Stilmar, U.S. Pat. No. 3,531,441 (1970) which describes the preparation of tri- and tetra-polymers comprised of VF, TFE and a vinylidene monomer having neither an aromatic group nor a halogen group attached to the vinylidene group in non-aqueous media. More recently, vinyl fluoride copolymers and vinyl fluoride interpolymers with low crystallinity have been described by Uschold in U.S. Pat. No. 6,242,547 (2001), U.S. Pat. No. 6,271,303 (2001), U.S. Pat. No. 6,403,740 (2002) and JP-C-2001-524146 (2001), Uschold in U.S. Pat. No. 6,242,547 proposes an interpolymer comprised of VF and at least two highly fluorinated monomers wherein at least one of the highly fluorinated monomers introduces a side chain having at least one carbon atom into the polymer. Such an interpolymer dissolves easily in some organic solvents because of decreased crystallinity, and also a film obtained from the interpolymer has low surface tension.
However, in the VF copolymers previously prepared, as fluorine content in the VF copolymer increases, the resulting resin tends to have lower intermolecular forces (intermolecular cohesive energy) and lower critical surface tension resulting in reduced adhesiveness to substrates, especially to metals and glass.
In addition, in order to improve processability, in particular, solubility of the polymer in an organic solvent, it is necessary to reduce the crystallinity or molecular weight of the VF copolymer. However, this results in reduced mechanical performance, thermal resistance and adhesiveness to substrates.